It’s Payback Time for Trees in Winter

In the summer, trees provide shade from blazing sunlight and help lower our air conditioner bills.  On top of that, these impressive plants absorb pollutants, such as carbon dioxide, from the air and emit oxygen so we can breathe more easily.

So in the winter, it’s payback time for trees. We need to look out for them the way they look out for us.

How? There are several ways:

Wrap trees to prevent sunscald and discourage frost cracking.  Protect your young, thin-barked trees by wrapping them in the fall, preferably around Halloween.  If you’re like me, you may not get around to it till November.  It’s still not too late to do it now before snow starts, causing reflection of sunlight off of snow and onto trees.  But get it done.  Then be sure to take the tree wrap off around Easter so insects don’t burrow under it and start munching or building nests.  CSU offers tree-wrapping tips.

This is what happens if you don’t wrap thin-barked trees when they’re young. Notice the vertical crack in the middle of this spring snow crab. The trunk has grown around the crack to seal it, but the tree is permanently disfigured.

Water trees once a month. Do this only when temperatures are above 40 degrees, and do it during mid-day so water has time to soak into the ground before freezing at night.  But don’t water where there’s snow on the ground.

Place a hose at the drip line (under the widest part of the tree canopy, where rain would drip from the branches to the ground) and let water trickle into the ground.  Move the hose periodically until you’ve gone all the way around the tree.  Evergreens, in particular, need winter watering because they lose water through their needles in dry air.

Notice the location of the green watering hose. It’s about three feet from the base of this little Tina dwarf crabapple tree because that’s where the drip line is. Also, notice the tree wrap around the trunk. As needed, keep trees wrapped and watered during the winter.

Prune trees when necessary, usually during dormant season.  Have you ever noticed all the broken branches after a major snowstorm?  Breakage usually results from poor tree maintenance.  That’s one reason it’s important to keep your trees pruned.

Winter is the best time to prune most trees, especially species that are susceptible to fire blight. I’m talking about apples, crabapples, pears, serviceberries and hawthorns, among others.

Also, after the leaves fall, you can assess a tree’s structure and problem areas more accurately before pruning.

Take good care of your trees in winter, and they’ll stick around to take care of you the rest of the year.

Discover the Cold, Ugly Truth about Sunscald and Frost Cracking

Sunscald discolored the bark on this young nursery tree. Wrapping the tree in late autumn would likely have prevented injury. (Photo courtesy of Robert Cox)

Now that trees have shed their leaves, you’ll likely notice their architectural splendor.  But you may also notice something else—disfigured trunks from sunscald and frost cracking.

What is sunscald?  “It’s essentially a sunburn, but it’s also got to do with the amount of water and moisture in the trunk,” explains Robert Cox, extension agent—horticulture with Colorado State University in Arapahoe County.  “(Sunscald produces) real obviously discolored bark, particularly on the south or southwest side of a young, non-native, deciduous tree.”

Sunscald-damaged bark may eventually crack or fall off in patches, maiming the tree trunk and leaving it vulnerable to diseases and insects.

Trees prone to sunscald include fruit trees, maples, oaks, ashes, lindens, honey locusts, beeches and willows.

Fortunately, you can reduce the risk of this problem, according to Cox, by protecting your young, deciduous trees that have south, southwestern or western exposure.  Wrap your youngsters with light-colored tree wrap in late fall, and then remove the wrap around mid-April.  Once they’ve grown old enough to produce furrows in their bark, you can then stop wrapping them.

For directions on tree wrapping, visit Colorado State University Extension’s website.

Frost cracking disfigured this stunning maple. Fortunately, wound wood is forming to cover the damage.

As for frost-cracking, here’s how it occurs.  A tree’s bark warms up on a sunny winter or early spring day.  The warmth causes the water in the trunk’s inner bark and in the wood to expand.  As the sun sets, temperatures drop quickly, causing the water to cool and contract. This rapid expansion and contraction can cause vertical cracks in the trunk.

Cox notes that maples, particularly Norway maples, are susceptible to frost cracking.  The only way to prevent frost cracking, he says, is to “plant trees that aren’t prone to frost cracking.  But that’s not really practical,” he points out.  “People are going to plant what they want to plant and deal with the consequences later.”

Trees prone to frost cracking include maples, crabapples, beeches, oaks, lindens, horse chestnuts and willows.

Once a tree has been injured by sunscald or frost cracking, the damage is permanent, though usually not fatal, unless insects or diseases move in and weaken the tree further.

What can you do if your trees fall victim to these two maladies?

“Try to increase its (the tree’s) vigor so that it produces wound wood–that growth you see developing after an injury like that,” explains Cox.  “Fertilize it (the tree) maybe in spring or early summer of the growing season; make sure it gets sufficient water; keep it watered during dry spells in the winter—anything you can do to keep it healthy so it does form that wound wood readily.”

Concerning trunk cracks, he adds, “Certainly, use of a fungicide wouldn’t be a bad idea.  It isn’t going to hurt anything to spray a liquid fungicide in that frost crack periodically just to make sure things don’t happen in there, because water’s going to get in there, snow’s going to melt and rain’s going to come into that wound.”